Monday, 28 April 2008

Using Google Charts with KML

In my last post, I showed how KML icon images could be utilised for proportional symbol mapping. Instead of loading a custom image, images can be requested from the URL based Google Chart API as shown below (download KMZ).

These pie charts are generated on-the-fly. The dataset is the same I used for my OpenLayers and Google Chart mashup. The charts are scaled according to total population and the pie shows the age distribution for each country. If you click on a chart, you'll see a larger version in the balloon:

Since the pie charts are loaded from an external service, the KMZ file is only 10 kB. There are some performance issues since around 200 pie charts are requested from the Google Chart API. I hope to see chart functionality as an integral part of KML and various geobrowsers in the future.

I was trying to use google charts api with Gearth but when its not showing any charts.I included the chart url in description tag and cannot see any output.Is there any specific way i need to follow while writing kml or creating charts.Could you also please suggest me how to make charts on the fly(i.e server side)

If you download the KMZ file in this blog post, you can right-click on an element in the places panel in Google Earth, select 'copy' and paste the code into a text editor. You'll then see how the chart images are referenced in KML.

To generate charts on the server you could use a graphics library like gd (complicated), or generate URLs for the Google Chart API (not so complicated). Details are explained in the Thematic Mapping Engine documentation (click on Downloads above).

HiThe problem is with labels in google chart URLs, for some reason the vertical bar separator makes the URL unusable. I've just tried your KMZ file with GE 4.3.7284.3916 - I have proper images for placemarks, but in the description only gray rectangles remain. If I remove labeling (legeng) from URL to google charts the image appears. Any ideas how to solve it?

Okay, this is pretty amazing; I've got to admit. But, how can we do this but get the stuff to load automatically... I would like to see this created, but the KML file come from autoprocessing the components of an SQL database. HAve you ever seen something like that?

Hi! Great example. Just wanted to comment that some data visualization snobs would point out the similarity between this and the pies-on-map graphic that VDQI. More info: http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=00018S

But I really respect what you were able to achieve with respect to the API.